Accidentally I bought the same book twice (kudos to Neal Stephenson ;o) - I financed his new private jet
).
One time in the The Confusion: Baroque Cycle, Vol. 2 and one time the The Confusion collection (including that book).
The problem was that I couldn't re-download either the single book or the Vol. 2 book in the collection.
Now I had a discussion with the hotline. First he didn't believe that it is possible to download the same ebook (indirectly) twice, but as I suspected this seem to be the problem.
If you want to tease somebody buy him (with your credit card and his account) the same book twice and he will be unable to re-download the ebook at all.
Anyway the support is (hopefully) looking in this issue so you propably don't have to too much time to have some fun
.